The invention relates to concentrated aqueous based surfactant compositions and especially to liquid laundry detergent compositions and toiletry compositions containing high concentrations of surfactant.
Liquid laundry detergents have a number of advantages compared with powders which have led to their taking a substantial proportion of the total laundry detergent market. The introduction of compact powders containing higher concentrations of active ingredient than the traditional powders has challenged the trend towards liquids. There is a market requirement for more concentrated liquids to meet this challenge, and in particular concentrated aqueous surfactant compositions containing dissolved or suspended builder salts.
The ability to concentrate liquid detergent has hitherto been limited by the tendency of conventional detergent surfactant systems to form mesophases at concentrations above 30% by weight, based on the weight of water and surfactant. Mesophases, or liquid crystal phases are phases which exhibit a degree of order less than that of a solid but greater than that of a classical liquid, e.g. order in one or two, but not all three dimensions.
Up to about 30% many surfactants form micellar solutions (L.sub.1 -phase) in which the surfactant is dispersed in water as micelles, which are aggregates of surfactant molecules, too small to be visible through the optical microscope. Micellar solutions look and behave for most purposes like true solutions. At about 30% many detergent surfactants form an M-Phase, which is a liquid crystal with a hexagonal symmetry and is normally an immobile, wax-like material. Such products are not pourable and obviously cannot be used as liquid detergents. At higher concentrations, e.g. above about 50% by weight, usually over some concentration range lying above 50% and below 80% a more mobile phase, the G-phase, is formed.
G-phases are non-Newtonian (shear thinning) normally pourable phases, but typically have a viscosity, flow characteristic and cloudy, opalescent appearance, which render them unattractive to consumers and unsuitable for use directly as laundry detergents. Attempts to suspend solids in G-phases have been unsuccessful, giving rise to products which are not pourable.
At still higher concentrations e.g. above about 70 or 80% most surfactants form a hydrated solid. Some, especially non-ionic surfactants, form a liquid phase containing dispersed micelle size droplets of water (L.sub.2 -phase). L.sub.2 phases have been found unsuitable for use as liquid detergents because they do not disperse readily in water, but tend to form gels. Other phases which may be observed include the viscous isotropic (VI) phase which is immobile and has a vitreous appearance.
The different phases can be recognised by a combination of appearance, rheology, textures under the polarising microscope, electron microscopy and X-ray diffraction or neutron scattering.
The following terms may require explanation or definition in relation to the different phases discussed in this specification: "Optically isotropic" surfactant phases do not normally tend to rotate the plane of polarisation of plane polarised light. If a drop of sample is placed between two sheets of optically plane polarising material whose planes of polarisation are at right angles, and light is shone on one sheet, optically isotropic surfactant samples do not appear substantially brighter than their surroundings when viewed through the other sheet. Optically anisotropic materials appear substantially brighter. Optically anisotropic mesophases typically show characteristic textures when viewed through a microscope between crossed polarisers, whereas optically isotropic phases usually show a dark, essentially featureless continuum.
"Newtonian liquids" have a viscosity which remains constant at different shear rates. For the purpose of this specification, liquids are considered Newtonian if the viscosity does not vary substantially at shear rates up to 1000 sec.sup.-1.
"Lamellar" phases are phases which comprise a plurality of bilayers of surfactant arranged in parallel and separated by liquid medium. They include both solid phases and the typical form of the liquid crystal G-phase. G-phases are typically pourable, non-Newtonian, anisotropic products. They are typically viscous-looking, opalescent materials with a characteristic "smeary" appearance on flowing. They form characteristic textures under the polarising microscope and freeze fractured samples have a lamellar appearance under the electron microscope. X-ray diffraction or neutron scattering similarly reveal a lamellar structure, with a principal peak typically between 4 and 10 nm, usually 5 to 6 nm. Higher order peaks, when present occur at double or higher integral multiples of the Q value of the principal peak. Q is the momentum transfer vector and is related, in the case of lamellar phases, to the repeat spacing d by the equation Q=2npi!/d where n is the order of the peak.
G-phases, however, can exist in several different forms, including domains of parallel sheets which constitute the bulk of the typical G-phases described above and spherulites formed from a number of concentric spheroidal shells, each of which is a bilayer of surfactant. In this specification the term "lamellar" will be reserved for compositions which are at least partly of the former type. Opaque compositions at least predominantly of the latter type in which the continuous phase is a substantially isotropic solution containing dispersed spherulites are referred to herein as "spherulitic". Compositions in which the continuous phase comprises non-spherulitic bilayers usually contain some spherulites but are typically translucent, and are referred to herein as "G-phase compositions". G-phases are sometimes referred to in the literature as L.alpha. phases.
L.sub.1 -phases are mobile, optically isotropic, and typically Newtonian liquids which show no texture under the polarising microscope. Electron microscopy is capable of resolving the texture of such phases only at very high magnifications, and X-ray or neutron scattering normally gives only a single broad peak typical of a liquid structure, at very small angles close to the reference beam. The viscosity of an L.sub.1 -phase is usually low, but may rise significantly as the concentration approaches the upper phase boundary.
M-phases are typically immobile, anisotropic products resembling waxes. They give characteristic textures under the polarising microscope, and a hexagonal diffraction pattern by X-ray or neutron diffraction which comprises a major peak, usually at values corresponding to a repeat spacing between 4 and 10 nm, and sometimes higher order peaks, the first at a Q value which is 3.sup.0.5 times the Q value of the principal peak and the next double the Q value of the principal peak. M-phases are sometimes referred to in the literature as H-phases.
VI-phases have a cubic symmetry exhibiting peaks at 2.sup.0.5 and 3.sup.0.5 times the Q value of the principal peak, under X-ray diffraction or neutron scattering. They are typically immobile, often transparent, glass like compositions. They are sometimes observed over a narrow range of concentrations, typically just below those at which the G-phase is formed.
The term "pourable hexagonal phase" is used herein to describe a phase exhibiting certain characteristic properties which include: pourability, often with an appreciable yield point, and a viscous, mucus-like characteristic and sometimes a lamellar flow pattern, resembling those normally observed with a "G" phase; birefringence; and a hexagonal symmetry typical of an M-phase, by small angle X-ray diffraction or neutron scattering. Some of these compositions tend to separate on prolonged standing into two layers, one of which is substantially clear, optically isotropic and substantially Newtonian in behaviour and the other an M-phase or G-phase.
Optical microscopy using crossed polars or differential interference constrast, typically reveals textures which may resemble either M-phase or G-phase or be intermediate, or alternate between the two on application and relaxation of shear. GB 2179054 and GB 2179053 describe compositions (eg, in the comparative examples) which appear to be in the pourable hexagonal phase.
The pourable hexagonal phase should be distinguished from aerated M-phase. Conventional M-phases containing substantial amounts of entrained air may sometimes exhibit properties similar to those described above as being characteristic of the pourable hexagonal phase. The former however revert to conventional non-pourable M-phases when de-aerated, eg, by centrifuging. The pourable hexagonal phases as herein defined exhibit the aforesaid properties even when substantially free from entrained air.
One possible explanation for the properties of pourable hexagonal phases is that they are compositions which exist normally in the M-phase but which are very close to either the M/G phase boundary or the L.sub.1 /M boundary (or which exhibit a broad, indistinct M/G or L.sub.1 /G phase boundary region), so that shear stresses convert them to G-phases. The pourable hexagonal phases are typically more dilute than conventional G-phases which typically occur at active concentrations above 50%, usually 60 to 80%. They are also more viscous in appearance than the G-phases which normally occur in the lower part of the above typical range.
L.sub.2 -phases resemble L.sub.1 -phases in general appearance but are less easily diluted with water.
A detailed description, with illustrations, of the different textures observable using a polarising microscope, which characterise the different mesophases, is to be found in the classic paper by Rosevear JAOCS Vol. 31 P.628.
All references herein to the formation or existance of specific phases or structures are to be construed, unless the context requires otherwise, as references to their formation or existence at 20.degree. C.
For the purpose of this specification "an electrolyte" means any water soluble compound which is not a surfactant and which ionises in solution. Preferred are electrolytes which tend to salt a surfactant out of solution when each is present in sufficiently high concentration, which are referred to herein as "surfactant-desolubilising electrolytes".
"Builder" is used herein to mean a compound which assists the washing action of a surfactant by ameliorating the effects of dissolved calcium and/or magnesium. Generally builders also help maintain the alkalinity of wash liquor. Typical builders include sequestrants and complexants such as sodium tripolyphosphate, potassium pyrophosphate, trisodium phosphate, sodium citrate or sodium nitrilo-triacetate, ion exchangers such as zeolites and precipitants such as sodium or potassium carbonate and such other alkalis as sodium silicate.
Detergents for laundry use normally contain a surfactant and a builder. The latter helps the surfactant to perform much more efficiently, thereby substantially reducing the amount of surfactant needed. Built liquid detergents contain about 5 to 15% of surfactant and 10 to 30% of builder.
In the absence of builder more than double the amount of surfactant may be required to obtain acceptable performance. Since the surfactant is considerably more expensive than the builder, the latter has been considered by some essential to cost effective performance.
The major problem with trying to include soluble builders in liquid detergents has been that such builders are electrolytes which tend to salt surfactants out of solution. The normal consequence of adding a salting-out electrolyte to an aqueous solution of an organic compound is to cause phase separation. This has commonly been observed in the case of aqueous surfactants and has given rise to a strong prejudice against adding electrolytes even to weak concentrations of aqueous surfactant in high enough concentrations to incur the likelihood of salting out. In the case of more strongly concentrated aqueous surfactant solutions, there has been an even stronger prejudice against adding electrolyte in any significant amount.
Typically commercial liquid laundry detergents fall into three main categories. The original liquid laundry detergents were aqueous surfactants, containing no more than low concentrations of water-soluble builder salts together with solvents and hydrotropes in order to overcome the salting effect of any electrolyte and maintain a stable, non-structured, isotropic, aqueous, micellar solution (L.sub.1 -phase). The performance of such products has been poor compared with powders. The performance per gram of product has been improved by formulating them at relatively high concentrations, e.g. up to 60% surfactant by use of more soluble, but more expensive surfactants in conjunction with sufficiently high levels of organic solvent. Because the latter do not contain high levels of builder they have to be dosed at higher levels than those which have customarily been needed for standard built products, in order to obtain comparable performance. The effect is to provide higher levels of surfactant in the wash liquor to compensate for the lack of builder. In addition the more soluble surfactants tend to be less effective as detergents. There is therefore little benefit in terms of the bulk required, and the disadvantage of a relatively high cost per wash, exacerbated by the higher cost of the soluble surfactants and the cost of solvent which is needed to maintain a homogeneous isotropic composition, but which does not contribute to wash performance. The high surfactant loading per wash and the presence of solvent is also disadvantageous on environmental grounds.
Progress from the early type of low-builder, clear liquids was for many years prevented by the knowledge that if the concentration of electrolyte salt is too high phase separation is observed. However it has been shown, e.g. in U.S. Pat. No. 4,515,704, U.S. Pat. No. 4,659,497, U.S. Pat. No. 4,871,467, U.S. Pat. No. 4,618,446 or U.S. Pat. No. 4,793,943 that when electrolyte is added to aqueous surfactants in concentrations substantially greater than the minimum concentration required to salt out any surfactant, then provided that there is enough of the latter present, instead of phase separation, a structured dispersion of surfactant in aqueous electrolyte is formed which may be stable and usually resembles either an emulsion or a gel.
This discovery led to the development of a second type of liquid detergent which comprised a suspension of solid builder, such as sodium tripolyphosphate or zeolite, in a structured aqueous surfactant. The surfactant structure is usually formed by the interaction of dissolved electrolyte with the surfactant. The latter is salted out of the isotropic micellar phase to form a mesophase interspersed with the aqueous electrolyte.
By suitable choice of electrolyte and surfactant concentration a stable mobile composition can be obtained, which maintains the solid particles of builder in suspension indefinitely. Because the builder level is high, the performance of this type of detergent at low surfactant level is good, giving a relatively low cost per wash, and environmental benefits from reduced usage of surfactant.
However the most effective solid builders have themselves been attacked an environmental grounds and are restricted or banned in some countries. Typical built liquid detergents have the further disadvantage of being relatively dilute, with surfactant concentrations typically in 5 to 15% range. This means that the consumer has to carry home a substantial bulk of product. Few attempts to increase the concentration of surfactant in the structured type of liquid detergent above about 20% have been made for fear of phase separation or unacceptable viscosity. Because the prejudice against adding electrolyte to concentrated surfactant is so strong the possibility of formulating aqueous pourable detergents with high surfactant levels and high levels of dissolved electrolyte has not been seriously considered as a practical possibility.
The third type of detergent, and the most recent to be introduced onto the market is an anhydrous type. This has the advantage of high surfactant concentration and also the possibility of including oxidising bleach which is normally difficult to include in aqueous formulations. However existing anhydrous formulations contain substantial amounts of organic solvent, which may be criticised on environmental grounds, and are difficult to dilute to wash liquor concentration. Addition of water tends to cause gel formation. The high concentration can give rise to a risk of overdosing. In addition the storage stability of this type of detergent is usually poor.
It is an object of the invention to prepare highly concentrated aqueous based structured liquid detergent or toiletry compositions which do not require the presence of solvents but which may contain high levels of surfactant that have only been available hitherto in solvent containing formulations. A particular object is to provide such compositions which are capable of suspending particles of solid or liquid, such as toiletry ingredients or builder. A further object is to provide mobile compositions containing high levels of surfactant and high concentrations of soluble builder. A further object is to provide concentrated detergents which are easily diluted to wash concentrations, without gel formation. It is also an object of the invention to provide aqueous structured surfactants capable of suspending functional solids such as pesticides, abrasives, dyes, weighting agents and the like.
Another object of the invention is to provide a liquid detergent which contains a high total payload of surfactant and builder.
The aim is to provide detergents that can be easily diluted to give stable and preferably clear semi-concentrated solutions which are readily dosed. Such compositions, would overcome the principal disadvantages of each of the three types of liquid laundry detergent currently on the market.
A further object is to formulate such detergents using surfactants based on renewable resources.
A further object of the invention is to permit the formulation of toiletry compositions containing suspended solids and water immiscible liquid. The stable suspension of various ingredients which are useful in toiletry, cosmetic, shampoo and topical pharmaceutical preparations has long been a goal of formulators. Hitherto this has proved difficult because the surfactants which are preferred for toiletry use have not been obtained as solid-suspending structures. Attempts to suspend solids by the use of polymers, clays and similar thickening agents add to the cost of the product without contributing to performance.
Currently available structured liquid detergents are typically based on alkyl benzene sulphonate, in admixture with smaller amounts of alkyl ether sulphate and/or alkyl sulphate and/or non-ionic surfactants such as alcohol ethoxylates, and/or mono or diethanolamides. Such mixtures are unsuitable for toiletry use. Attempts to formulate highly concentrated suspensions using these systems, based on existing technology have been unsuccessful. Such mixtures, typically have a relatively high cloud point and are relatively insoluble in dilute aqueous electrolyte solution.
This indicates that they are comparatively easily forced into a solid-suspending structure by electrolyte. In solution they form clear, isotropic, mobile L.sub.1 micellar solutions at concentrations up to about 30% by weight. At higher concentrations they form immobile M-phases, and at still higher concentrations G-phases and VI-phases may be observed.
When electrolyte is added progressively to conventional L.sub.1 surfactant systems of the above type, a sequence is observed which is described in U.S. Pat. No. 4,618,446. Initially, if the surfactant is sufficiently dilute, e.g. below about 30% by weight, a clear, isotropic, micellar solution is formed. Addition of electrolyte at first causes an increase in conductivity.
Further additions cause turbidity due to the formation of surfactant spherulites which separate on standing to leave a clear aqueous layer containing electrolyte and an opaque surfactant layer. It is envisaged that the spherulites form by the deposition of successive bilayers of salted-out surfactant on the spherical micelles present in the L.sub.1 -phase.
With further additions of electrolyte the spherulites become more numerous. They form clusters separated by clear areas. The proportion of the surfactant layer formed on separation increases, while the electrical conductivity falls.
Eventually a packed mass of spherulites is formed with no visible clear areas. The composition no longer undergoes separation, but remains homogeneous and opaque, even on prolonged standing. At this stage the composition is highly structured with a marked yield point and can suspend solid particles indefinitely.
After further additions of electrolyte the electrical conductivity passes through a minimum and then rises. At the same time the average size of the spherulites declines while their number appears to be approximately constant. Clear areas appear again and the system is no longer solid-suspending.
Subsequently, if the dissolved electrolyte concentration is increased further, the conductivity may pass through a further point of inflexion and falls again to a second minimum. The second minimum is associated with the formation of an open lamellar structure which is believed to comprise a reticular lamellar phase forming a three dimensional network interspersed with a substantially surfactant-free aqueous electrolyte solution (often referred to as a lye phase).
Thus in the classical built liquid detergents two types of suspending system can be distinguished.
I. A spherulite system, associated with a first (lower electrolyte) trough in the plot of conductivity against dissolved electrolyte concentration, is at its most stable near the first conductivity minimum. It comprises spherulites which range typically between 0.1 and 20 microns in size and each having an onion like structure comprising a series of concentric spherical layers, each layer consisting of a bilayer of surfactant separated from neighbouring layers by an intermediate spherical shell of water or lye. Such systems are formed by surfactant/water systems which form spherical L.sub.1 solutions in the absence of electrolyte. Most built liquid detergents in commercial use are of this spherulitic type. PA1 II. A lamellar system, which may be associated with a second (higher electrolyte) conductivity trough, as a weak three dimensional reticular structure interspersed with lye. It is typically more viscous than the corresponding spherulitic system at comparable surfactant concentrations. Because of the relatively high viscosity these reticular lamellar systems have had more limited application.
Now discovered are detergent and toiletry formulations that provide stable, homogeneous pourable compositions at eg, surfactant concentrations in the range 20 to 70%, or higher, certain of which are capable of suspending solids such as builders and/or cosmetic, toiletry or pharmaceutical ingredients and which typically can be diluted without gel formation.